In multi-step motor vehicle automatic transmissions known in practice, shifting elements in the form of wet clutches or brakes are used for engaging various gear ratio steps between a transmission input shaft and a transmission output shaft of the automatic transmission. For this purpose, depending on the gear ratio step desired, the shifting elements are opened or closed. In most cases the pressure force required for that is applied, for each shifting element, by a hydraulically actuated clutch piston which is supplied with hydraulic fluid by way of shifting element valves, also known as pressure reducing valves. These pressure reducing valves are either themselves designed as proportional pressure control valves, or are actuated by hydraulic pilot control wherein the hydraulic pressure required for the pilot control is again set by a proportional pressure control valve. In such a proportional pressure control valve, depending on an energizing current a magnetic force is produced, as a function of which a certain predictable working pressure is set at the valve. This pressure can be tapped from an outlet area of the valve and is determined by the ratio between the magnetic force (the action force) and a return force of the valve directed in opposition to the magnetic force (the reaction force).
The proportional pressure control valves commonly encountered today, for example that described in WO 2005/026858 A1, comprise two seat valves coupled in a hydraulic semi-bridge circuit, i.e. they have one inlet area and two outlet areas, such that in terms of flow a first seat valve is arranged between the inlet area and the first outlet area and a second seat valve is arranged between the inlet area and the second outlet area. In this case the seat valves are designed, and their closing elements are coupled to one another, in such manner that in their end positions the closing elements close or open the seat valves alternately.
To reduce the flow resistance and increase the ability of a transmission shifting element controlled by the pressure control valve to be dynamically regulated, in WO 2005/026858 A1 a flow-guiding device is proposed, to be specific a stream deflector between the first and second outlet areas, which deflects a fluid flow from the first seat valve to the second seat valve by less than 30°.
From WO 20091092488 A1 it is also known to provide such a flow-guiding device with a plurality of channel areas in such manner that a swirling motion is imparted to the fluid flowing in the direction of the second seat valve, which improves the valve dynamics and reduces the valve leakage.
With these pressure control valves known from the prior art, pressure fluctuations can occur on the inlet or outlet side which, for example, result from pump pressure fluctuations or slip-stick effects in the shifting elements of a vehicle transmission, and which act almost without impediment on the closing elements of the seat valves, which makes it more difficult to set a measurable working pressure at the valve.